This invention relates generally to a noise suppression panel, and more particularly, but not by way of limitation, to a sandwich structure having a first imperforate facing sheet adhered to one surface of a first honeycomb core, a sheet of microporous material adhered to the other surface of the first honeycomb core, one surface of a second honeycomb core is adhered to the other surface of the first sheet of microporous material and its other surface is adhered to a perforated facing sheet with a second sheet of microporous material adhered to the opposite surface of the perforated sheet.
In the manufacture of sound suppression materials of this general type which are to be exposed to an extreme environment and to the sound produced by modern turbine aircraft engines, it is a common practice to provide a cellular structure utilizing the Helmholtz resonator principle. Examples of this type of material can be found in U.S. Pat. Nos. 2,952,579; 3,166,149; 4,111,081; 4,254,171; 4,269,882; 4,291,079; and 4,292,356. Examples of sound suppression panels utilizing double cellular structures can be found in U.S. Pat. Nos. 4,271,219 and 4,294,329.
The latter two examples work successfully but because of their method and materials of construction are costly to produce and have substantial weight.
The present invention provides an improved sound suppression panel with structural integrity and the capability of withstanding severe environmental conditions such as those encountered in and around modern turbine engines and is relatively inexpensive to construct and light in weight.